1. Field of the Invention
The present invention relates to an improvement of a club head for an iron-type golf club.
2. Description of the Related Arts
Generally, a club head of an iron-type golf club for relatively inexperienced players should have a wide sole enabling an easy and smooth swing and to have a lower position of center of gravity thereof to easily obtain a high trajectory of flight of a ball. Further, the depth of the center of gravity of such a club head should be farther from the striking surface thereof and the moment of inertia thereof about the vertical axis passing through the center of gravity thereof should be increased in order to stabilize the direction of flight of a ball. On the other hand, such a club head also should have a shape such that the distance of flight of a ball is increased. However, when designing a club head that will meet the above-mentioned requirements, it is necessary to consider the restrictions in the total weight and loft thereof.
Japanese Patent Publication No. 38-19176 discloses a conventional iron-type golf club in which a club head having a nearly L-shaped cross-section includes a front wall section having a front side for hitting a ball, and a sole wall section. In the head of this type, the front wall section has a nearly constant thickness and is inclined backward from the bottom end toward the top end thereof to define a loft angle depending on a club number, and the sole wall section has a nearly constant thickness and extends backward from the bottom end of the front wall section. According to such a conventional club head having a nearly L-shaped cross-section, it is easy to increase the width of the sole wall section between the bottom end of the front wall section and the rear end of the sole wall section and the depth of the center of gravity thereof from the front surface of the front wall section and to lower the position of center of gravity of the head, while taking into consideration the restrictions of the total weight and loft of the head.
However, such a conventional head having a nearly L-shaped cross-section has a disadvantage in that the front wall section is easily distorted when hitting a ball, and thus the distance of flight of a ball hit by this head is decreased. Further, since the thickness of the front wall section of such a head having a nearly L-shaped cross-section is relatively thin around an impact point of the head, i.e., a point at which the head is initially in contact with a ball when the club head of the golf club is normally swung, it is difficult to effectively transfer the kinetic energy of the head to the ball, and thus the distance of flight of a ball hit by the head is shortened.
Japanese Utility Model Publication No. 55-65059 discloses a club head for an iron-type golf club which is similar to the above-mentioned club head having a nearly L-shaped cross-section, except that the thickness of the sole wall section gradually increases from the rear end thereof toward the front wall section, and thus the distribution of weight of the head is concentrated around the impact line of the head to a certain degree. Accordingly, it is possible to effectively transfer the kinetic energy of the head to a ball.
However, in the club head disclosed in Japanese Publication No. 55-65059, since the sole wall section has a cross-section having a right-angled triangle without any bore therein, it is difficult to increase the depth of the center of gravity of the head from the front surface thereof and to increase the moment of inertia about the vertical axis passing through the center of gravity of the head, and thus the direction of flight of a ball hit by the head is sometimes inaccurate.
A hollow metal head for an iron-type golf club is also known. Such a hollow metal head includes a front wall section having a front side for hitting a ball, a sole wall section extending backward from the bottom end thereof, and a back wall section extending from the top end of the front wall section to the rear end of the sole wall section. The front, sole, and back wall sections of the hollow metal head have nearly constant thicknesses, respectively, and define a closed cavity. According to the construction of such a hollow metal head, it is easy to increase the depth of the center of gravity of the head from the front side of the front wall section and the moment of inertia of the head about a vertical axis passing through the center of gravity of the head, and accordingly, the direction of flight of a ball hit by the head can be stabilized.
However, in such a hollow metal head, since there is a cavity behind the impact point of the head, the front wall section of the head is distorted when hitting a ball, and thus the distance of flight of a ball hit by the head is shortened. Further, since the weight of the head is low at the back of the impact point of the front wall section of the head, it is difficult to effectively transfer the kinetic energy of the head to a ball, and accordingly, the distance of flight of a ball hit by the head is shortened. Furthermore, since the back wall section extends to the top end of the front wall section, and thus the weight of the back wall section is increased, the center of gravity thereof is raised, and the width of the sole wall section between the bottom end of the front wall section and the bottom end of the back wall section is reduced due to the restriction in the total weight of the head. Accordingly, such a hollow metal iron type head has a disadvantage in that the trajectory of flight of a ball hit by the head is not stable, and it is difficult to ensure a smooth swing of the head.